Motorcycle displacement issues...

[JackD]

Many, many, moons ago we had a 1300 c.c. class.....I ran a big bore KZ
Kawa that I knew was 1260c.c......
the oil-pump method showed it to be over 1300c.c.....had to tear the motor down to show I was right (1260c.c.) so how accurate is the oil-pump.....is it better these days? Or do they now know what they are doing???  Lets hope so !!!

It is only as accurate as your leak down will permit.
If you can cc a chamber accurately you will understand.

[JackD]

Sum, my request was for a modified bike.

My question now is: If I got my request turned down by Tech to build a 656cc bike to run in 650 based on "it doesn't fall within the spirit of the overbore rule, which was designed to allow a re-bore of old cylinders"  WTF are all these 1363 Busa's doing running in the 1350 class?  Looks like a double standard to me.

The production guys (me included) didn't want the overbore rule. It was some guy running a Flathead Harley who couldn't find new cylinders.

It was a 1 lung 2 smoke guy. It is common practice to re sleeve an old HD for example to get better material and improved strength. It was put forward by Dale Martin and laughed out of the room by the board when it was pointed out to them and the next year it got by them.
It is a bad rule that never should have happened.

[1212FBGS]

yama
ya must have asked the wrong person. I ran a bored 600 block on my gsxr 750 cases to set a record in my bike 'liner. the only way that would not be legal would be in the production class.
kr

[JackD]

When did the 650  a few open bike ever measure below 650 and the class limit?
The liner measured how big again ?
The overbore allowance,why does it not apply to the Production class, isn't it just as not valid ?

[1212FBGS]

649 john made my pistinz. compression was bout 17-1. cronking pressure was over 270. the thing hauled ass

[JackD]

Over 650 would have made it a little tough.

[jprovo]

What a strange rule?
Running some numbers on it, it basically gives you a 1-3% tolerance for engine displacement based on engine configuration. And as much as a 5% for a weird engine configuration like a 50cc four cylinder with a Stroke that?s twice the Bore?

If I interpret it correctly, for my engine with a 3.5? bore and a 3.125? stroke we get:

For production I can bore the motor to 3.5258? (3.500?+.0258?) and stay legal for production at 500cc.
3.5258?^2*3.125*pi/4 = 499.75cc
Since I can?t find a +.025? piston, I can go with a +.015? or +.020? piston that?s commonly available and be under 500CC and still OK for Production.

Conceivably, I can then bore the motor .020? more than 3.5258? and be within 500cc altered or modified rules (but not Production).
3.5458?^2*3.125*pi/4 = 505.68 cc
Which gives me a 1.14% increase over 500cc. Of course, finding a +.0458? piston is again going to be impossible without getting some made, so I?d have to settle for a commonly available +.030 piston which will give me a 501cc engine.

The 501cc engine will be legal for 500cc A or M, but here is where I?m confused. Is it illegal for 650 because it?s not over the maximum for 500 for this particular engine configuration?? My brain says It?s illegal for 650 in this configuration (I?d need to get a piston bigger than 3.5458?), but my gut?s telling me that I?d get away with it.

I also wonder how much of a hassle it?s going to be trying to explain why a +.030? engine is legal under the +.020? rule, but I digress?

[JackD]

Your mistake was to apply logic to the rule after thinking about it.
The origin and continued application of the rule speaks to the level of understanding , selective enforcement, and benefit it has for some.
There are worse things that represent even less thought.

[Hans Blom]

looks like i'll be destroking and staying in M or a class. ..thanks for all the input guys...

[1212FBGS]

jprovo,
you can run your motor in the 500cc class and the over displacement will be noted in the log book. set all the 500cc records you can and then call your motor a 650cc and run on those records. altho you may be at quite a big disadvantage. you are over the allowable displacement making it legal for the next bigger class. funny and weird but hey well take it if the let us. they dont let the car boys get away with it.
kr

[landracing]

Sorry to inform you, I already asked the question on the .010 overbore rule. they would not allow you to move into the next class if you claimed overbore for next lower class. The overbore rule is only for stock motors that don't have room.

For instance Joe's Zx10 motor is 998 stock. to allow for minor reconditioning of cylinders they allow .010 for cylinder cleanup. I was told that this will not put you into the next class... Orginally the .010 overbore rule was for vintage stuff where replacement parts are not available.

I would think there might be some problems with that in tech...

I already asked and been down that road... I wanted to do that with my ZX6. Stock I am 598cc... I said ok then if you allow overbore to cylinder reconditioning I would go .010 over 650cc then run in next class.. This was several years ago...

Now thats all based on how one interprets the rules, and I was told I was not in spirit of the rule... You know the unwritten rule... The ones that bite you in the ass in tech inspection... Just when you think you have intpreted something and made a pretty good assumption only to be shot down...

Now my thoughts have changed... There is only one record I want, and thats a fast one... not interested in the class changing deal...

Jon

[Salty Blaster]

jprovo your math is right, but you will run the risk of problems in tech or impound if you jump classes. As you know there is a direct bolt on 515 kit for the blast that will do the trick without splitting the cases. With a little pre planning you could grow your motor on the salt although you will have plenty other things to worry about your first time out   .

By the way, welcome to the board ... I've seen your post on the Buell thumper site before. All these class permutations can be a disease you know? Just to let you know your not alone, I've remained silent on the thump er site as our development work proceeds but I'll give you a sneak peek at our new play toy.

Good luck with your plans jprovo.

[Nortonist 592]

2005 rule book,  production class.   "OEM engine displacement determines the displacement class for competition.  Displacement may not be increased beyond that class limit."

[JackD]

you stroke it .010 longer with an offset grind you are a 650.
Who is the joke on ?
 

[Nortonist 592]

The way this thread is fudging around the rules I think if we did'nt have bikes we'd definitely have roadsters.